Tilting chair

ABSTRACT

A tilting chair comprising: a support board integrating its seat and back support to be elastically transformable backwards when a user puts pressure onto its back support; a frame that further consists of: a back support part tightly, horizontally coupled at the external surface of the back support, a pair of rear legs extended from both left and right sides of the back supporting part downwards to the floor, a pair of feet bent at edges of the rear legs and extended forwards along the floor surface, a pair of front legs extended upwards from the front edges of the feet, a seat front side support part bent and extended to face at both upper ends of the front legs to support front portion of the seat, and a seat rear side support part interconnecting the center of the rear legs to support the rear portion of the seat; and flanges and coupling units respectively assembled at the external surface of the back support part and at the lower surface of the seat, to thereby make a user feel comfortable because a back support is smoothly tilted backwards when the chair is tilted, to easily control its tilting strength and range depending upon the user and to maintain its tilted angle with even a small degree of strength.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a chair, and more particularly to a tilting, public chair.

[0003] 2. Brief Description of the Prior Art

[0004] In general, an office chair is bi-classified into an individual office chair mostly used at personal business offices or study rooms and a public chair used at large-scale space like a conference or lecture room.

[0005] Most of the former individual office chair has a tilting function to reduce a user's fatigue of a long hour work by getting its back tilted backwards when a user leans onto the back of the chair. In order to include the tilting function as such, a chair should be made in a particular tilting structure with addition of a spring or other resilient materials according to a complicated manufacturing process.

[0006] On the other hand, the latter public office chair is made by firmly coupling back supporting board and seat with its supporting frame. As a result, it has only a function to be seated and low price, but it fails to offer any comfort to a user.

[0007] Therefore, the conventional public office chair has a problem of making a long hour sitting user very tired because the back supporting board is not tilted at all.

[0008] Besides, even if the user stretches his body backwards to relieve his physical strain, only neck part will be stretched out due to a fixed shape of the back supporting board which reduces the stretching effect without relief of the user's exhaustion.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to solve the aforementioned problem and provide a tilting chair whose frame can be modified and tilted by letting its back supporting board tilted backwards, to thereby help a user to effectively stretch himself backwards and to easily relieve fatigue.

[0010] It is another object of the present invention to provide a tilting chair that has a function to easily control its tilting strength and range depending upon a user and that can maintain its tilted angle with even a small degree of strength.

[0011] It is still another object of the present invention to provide a tilting chair whose shelf for putting on user's material and writing board can perform its original function without affecting tilting function.

[0012] In order to accomplish the aforementioned objects of the present invention, there is provided a tilting chair comprising:

[0013] a support board integrating a seat and a back support to be elastically transformable backwards when pressure is applied to the back support;

[0014] a frame which comprises a back support part tightly, horizontally coupled at the external surface of the back support, a pair of rear legs bent downwards and extended at both left and right sides of the back support part, a pair of feet bent at edges of the rear legs and extended forwards, a pair of front legs extended upwards from the front edges of the feet, a seat front side support part bent and extended to face at both upper ends of the front legs to support front portion of the seat, and a seat rear side support part interconnecting the center of the rear legs to support the rear portion of the seat;

[0015] flanges longitudinally coupled at the bottom surface of the seat;

[0016] a first coupling unit mounted at the front side of the flanges to fix the seat front side support part; and

[0017] a second coupling unit mounted at the rear side of the flanges to fix the seat rear side support part;

[0018] wherein the second coupling unit has a head part, a tail part and a hitching protruder formed at the end of the tail part to allow the seat rear side support part to slide along the tail part within a range between the head part and the hitching protruder.

[0019] The chair further comprises:

[0020] a flange unit mounted on the external surface of the back support and formed with a plurality of flanges positioned at a predetermined interval;

[0021] a pair of bushes fit with the flange unit and releasably coupled each other to insert the back support part therebetween; and

[0022] a third coupling unit having a plurality of wings to be tightly fit between the flanges of the flange unit.

[0023] Furthermore, the back support of the support board comprises a plurality of long holes formed to make a user easily lift the chair; a concave part is formed at a portion where the seat and back support meet and grooved to horizontally face each other to allows the back support to easily transform when the back support is applied to pressure; and the front end of the seat of the support board is formed with a downwardly curved surface to prevent the front end of the seat from pressing onto the user's thigh. Pairs of shoes are respectively coupled at both sides of the feet with hitching protruders formed to face each other for easy hitching of another chair.

[0024] The chair further comprises;

[0025] a front horizontal part extended in parallel to the seat front side support part from the center of the front legs; and

[0026] a shelf whose a front portion is hitched to the front horizontal part and a rear portion is hitched to the seat rear side support part;

[0027] wherein the shelf further comprises horizontal hitching racks hitched to the front horizontal part and rear hitching racks rotatively coupled with a vertical part at the rear side of the horizontal hitching racks and hitched to the seat rear side support part.

[0028] Furthermore, a pair of horizontally extended parts is extended to a predetermined length in parallel to the seat at both left and right ends of the back support part; the pair of rear legs is extensively bent toward the floor from the end of the horizontally extended parts; a support rack is coupled at a part where the seat front side support part and the front leg meet and extended upwardly to the height of the horizontally extended part, a writing board is coupled at the horizontally extended part and the support rack for easy writing; the upper portion of the support rack is coupled with the writing board by a first fixing bracket; the horizontally extended part is coupled with the writing board by a second fixing bracket, the first fixing bracket is restricted on a relative movement with the support rack by using the protruder formed at the support rack when the chair is tilted; and the second fixing bracket is coupled to relatively slide with the horizontally extended part when the chair is tilted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Objects and aspects of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings in which:

[0030]FIG. 1 is a perspective view for illustrating a tilting chair;

[0031]FIG. 2 is an exploded, perspective view of the tilting chair shown in FIG. 1;

[0032]FIG. 3 is an elevation of a tilting chair in accordance with a first embodiment of the present invention;

[0033]FIG. 4 is a perspective, exploded view for illustrating in detail a coupling part of the seat and frame shown in FIG. 1;

[0034]FIG. 5 is a perspective, exploded view for illustrating in detail a coupling part of the back support and frame shown in FIG. 1;

[0035]FIG. 6 illustrates tilting states of a tilting chair in accordance with the first embodiment of the present invention;

[0036]FIG. 7 is a perspective view for illustrating a tilting chair in accordance with a second embodiment of the present invention;

[0037]FIG. 8 is an exploded view of a tilting chair in accordance with the second embodiment of the present invention;

[0038]FIG. 9 is a sequential view for illustrating assembling steps of a shelf onto FIG. 7;

[0039]FIG. 10 is a perspective view for illustrating a tilting chair in accordance with a third embodiment of the present invention;

[0040]FIG. 11 is an exploded perspective view for illustrating a tilting chair in accordance with the third embodiment of the present invention;

[0041]FIG. 12 illustrates a tilting chair with its writing board put aside in accordance with the third embodiment of the present invention;

[0042]FIG. 13 illustrates a coupling state of the support rack shown in FIG. 11;

[0043]FIG. 14 is a cross-sectional view cut along arrow-marked line A-A shown in FIG. 13;

[0044]FIG. 15 is a cross-sectional view cut along arrow-marked line B-B shown in FIG. 13; and

[0045]FIG. 16 illustrates a tilting state of a tilting chair with its shelf and writing board coupled altogether.

DETAILED DESCRIPTION OF THE INVENTION

[0046] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to accompanying drawings.

[0047]FIGS. 1 and 2 are respectively a perspective view and an exploded, perspective view for illustrating a tilting chair in accordance with a first embodiment of the present invention.

[0048] As shown in the drawings, the tilting chair of the first embodiment of the present invention is constructed with a back support 32, a seat integrated with the back support 32 board 34, a support board 34 for being elastically transformable backwards when a user puts pressure onto the back support 32 and a frame 36 to support/maintain the support board 34.

[0049] At this time, the frame 36 is made of an elastic metal rod, including: a back support part 38 tightly, horizontally coupled at the external surface of the back support 32; a pair of horizontally extended parts 40, 40′ extended to a predetermined length in parallel to the seat 30 at both left and right ends of the back support part 38; a pair of rear legs 42, 42′ bent and extended from the ends of the horizontally extended parts 40, 40′ downwards to the floor surface, a pair of feet 44, 44′ bent at edges of the rear legs 42, 42′ and extended forwards along the floor surface, a pair of front legs 46, 46′ extended upwards from the front edges of the feet 44, 44′, a seat front side support part 48 bent and extended to face at both upper ends of the front legs 46, 46′ to support the front portion of the seat 30 and a seat rear side support part 50 interconnecting the center of the rear legs 42, 42′ to support the rear portion of the seat 30.

[0050] Arm support 52, 52′ are covered over the pair of horizontally extended parts 40, 40′ and shoes 54 are fit at both sides of the feet 44, 44′ for easy alignment of chairs without a direct touch on the floor.

[0051]FIG. 2 illustrates no coupling unit to be the support board 34 coupled with the frame 36.

[0052] As shown in FIG. 3, the support board 34 has a front end of the seat 30 downwardly curved surface to make a user feel more comfortable when his thigh touches the front end of the seat 30. Furthermore, a concave part 56 is formed at a portion where the seat 30 and the back support 32 meet, as seen from the lateral side of the chair. The concave part 56 is bent rearward to be easily deformed and not to be damaged when user puts pressure onto the back support with his back 32. Besides, the concave part 56 can make the back support 32 more flexibly transform the shape of the chair.

[0053] In addition, the concave part 56, as shown in FIG. 2, is grooved to horizontally face each other, which allows the back support 32 to easily transform when the user puts pressure onto the back support 32 with his back.

[0054] At this time, the seat 30 and the back support 32 are respectively shaped in a curved surface, suitable for a user's hip and back.

[0055] A pair of flanges 58, 58′ are mounted at the bottom surface of the seat 30 along with its length direction and coupled with the seat front side support part 48 and the seat rear side support part 50 of the frame 36. The pair of flanges 58, 58′ are formed at two positions to the horizontal direction of the seat 30. The pair of flanges 58, 58′ are positioned with an width interval so that first and second coupling units, which will be described below, can be put therebetween.

[0056] A plurality of horizontally shaped long holes 60 are formed at the back support 32 and the concave part 56 at a predetermined interval along the height direction of the back support 32.

[0057] Furthermore, two flange units 64 having a plurality of flanges 62 are mounted on the external surface of the back support 32 with a predetermined interval along with the width direction of the back support 32 to be coupled with back support part 38. The flanges 62 have a width interval so that each wing of a third coupling unit, which will be described below, can be fit into therebetween.

[0058] The back support part 38 of the frame 36 is formed in a shape of a curve, identical to an external shape of the back support 32. If the horizontally extended part 40 of a chair is long, it is difficult to put many chairs together. Therefore, it is preferable that the length of the horizontally extended part 40 is ⅓ of the length of the seat 30.

[0059] The seat front side support part 48 and the seat rear side support part 50 are roughly at the same level of their height. At this time, the seat rear side support part 50 is slightly protruded at the rear legs 42, 42′ to their lower, left direction and extended in parallel with the seat front side support part 48.

[0060] The arm supports 52, 52′ and shoes 54, 54′ are made of a plastic material with their longitudinal groove slots 68, 66, whose diameter is identical to that of the rod frame 36 to fit onto the horizontally extended parts 40, 40′ and the feet 44, 44′. At this time, the cross-section of the groove slots 68, 66 are formed with an arc, slightly larger than a semicircle. Therefore, if the arm supports 52, 52′ and shoes 54, 54′ are pushed with their groove slots 68, 66 onto the rod of the horizontally extended parts 40, 40′ and feet 44, 44′, the groove slots 68, 66 of the plastic arm supports 52, 52′ and shoes 54, 54′ are easily widened for easy insertion, but no detachment due to elasticity of a plastic material.

[0061] At this time, the shoes 54, 54′ are respectively coupled at both sides of the feet 44, 44′, and protruders 69, 69′ are formed at the lateral sides of the shoes 54, 54′. The hitching protruders 69, 69′ coupled at both sides of the feet 44, 44′ are formed to face each other, thereby getting easily hitched to shoes of other chairs.

[0062]FIG. 4 is an exploded, perspective view for illustrating a coupling part of the seat and frame as seen from the bottom of the seat.

[0063] As shown in FIG. 4, a first coupling unit 70 is fit between the front sides of flanges 58, 58′ at the lower side of the seat 30 for coupling the seat front side support part 48 and fixed with fastening members 72. Furthermore, a second coupling unit 74 is fit between the rear sides of flanges 58, 58′ for coupling the seat rear side support part 50 and fixed with fastening members 76.

[0064] A groove 78 whose rear side is straight inclined and the front side forms circular arcs, is formed at the front side of the flanges 58, 58′ for the seat front side support part 48 to be easily accommodated and hitched. A hitching part 80 is formed at the rear portion of the flanges 58, 58′ for seat rear support part 50 to be supported without being pushed forwards. The rear portion of the hitching part 80 has a low part for easy assembly of the seat rear side support part 50.

[0065] The first coupling unit 70 has convex portions at its sides and a concave portion at its center. The seat front side support part 48 is inserted into the concave part. The second coupling unit 74 has a tail part 81 from its head to its rear side. A hitching protruder 83 is formed at the end of the tail part 81 to restrict a range where the second coupling unit 74 can slide, so that the seat rear side support part 50 is hitched at a part where the head and tail part 81 meet. Thus, if the second coupling unit 74 is coupled, the external surface of the tail part 81 is a little protruded slightly higher than the rear portion of the hitching part 80 of the frame.

[0066]FIG. 5 is a perspective, exploded view for illustrating a coupling part of the back support and frame of the present invention as seen from behind the back support.

[0067] As shown in FIG. 5, the flange units 64 consisting of a plurality of flanges 62 formed at the external surface of the back support 32 is shaped with a ridge at two sides thereof and a valley at the center thereof. In the preferred embodiment of the present invention, there are three flanges 62 in the flange units 64.

[0068] A pair of bushes 82, 82′ are detachably inserted at the valley of the flange units 64, while the back support part 38 of the frame is fit between the bushes 82, 82′. The third coupling unit 84 is fixed at the flange units 64 with fastening members 86, while wrapping the bushes 82, 82′.

[0069] A protruding part 88 is formed at the external surface of the bush 82 to be inserted at interval C between the flanges 62. A hitching hole 90 is formed at the one side of the bush 82 to hold a hitching protruder 94 which will be described below. Furthermore, a protruder 92 is formed at the external surface of the bush 82′ to be hitched to a groove (not shown here) in the second coupling unit 84. The hitching protruder 94 is formed at the one side of the bush 82′ to be hitched into the hitching hole 90 of the bush 82. In addition, the aforementioned bushes 82, 82′ are made of acetaldehyde injection molds.

[0070] The third coupling unit 84 is shaped like a halfmoon as seen from its lateral side, including a plurality of meshing wings 96 formed at both sides thereof to mesh with the ridge of the flange units 64 and a fastening hole 98 to which the fastening members 86 are fastened.

[0071] As shown in the tilting chair in accordance with the first embodiment of the present invention, if a user leans onto the back support 32 to put pressure, the shape of the chair changes from a straight line state to its dot line state, as shown in FIG. 6.

[0072] In other words, as the back support 32 is tilted backwards, the front leg 46 and rear leg 42 are pushed apart to the opposite directions from both ends of the feet 44 of the frame 36. Elasticity of the frame 36 and of the support board 34 brings about tilting strength, and the back support 32 maintains its curved shape. As a result, a user feels comfortable without any pressure onto his back even when the chair is tilted.

[0073] When the chair is tilted, the seat rear side support part 50 slides along the external surface of the tail part 81 of the second coupling unit 74 to support the back side of the seat 30 and the user's weight. Also, the frictional force, that generates when the seat rear side support part 50 slides, gets to control the tilting strength because it increases or decreases depending upon the user's weight. If the seat rear side support part 50 slides at a predetermined angle, it is hitched by the hitching protruder 83, thereby restricting the tilting range.

[0074] Therefore, the seat rear side support part and the second coupling unit prevent the back support from excessively tilting backwards by restricting the tilting range. At this time, the back support part 38 is pivoted against the back support 32.

[0075] In addition, a constant level of friction remains between the seat rear side support part 55 and the second coupling unit 74, so that a level of strength is not required to maintain a certain degree of tilting angle. The aforementioned phenomenon can be understood with a resilience offset of the back support, which is technically named an indefinite locking effect.

[0076] The back support part 38 is pivoted against the back support 32 when the chair is tilted. At this time, the back support part 38 is shaped in a curve, but a pair of the acetaidehyde bushes 82, 82′ partially form a straightly moving range around the same axle to thereby prevent friction and abrasion of the pivot.

[0077] Furthermore, hitching protruders of another chair are inserted into the hitching protruders 69, 69′ of the shoes 54, 54′ fit onto the feet 44, 44′ for an easy alignment.

[0078]FIGS. 7 and 8 are respectively a perspective view and an exploded, perspective view for illustrating a stackable, tilting chair in accordance with a second embodiment of the present invention.

[0079] As shown in the drawings, in the second embodiment of the present invention, a shelf 100 is mounted under the seat 30 of the first embodiment of the present invention to conveniently put a user's belongings.

[0080] In other words, a front horizontal part 102 is extended in parallel to the seat front side support part 48 from the center of the front legs 46. The shelf 100 is coupled with its front portion being hitched to the front horizontal part 102 and with its rear portion being hitched to the seat rear side support part 50.

[0081] The front horizontal part 102 is bent to the rear in a curved shape.

[0082] Besides, in the shelf 100, lengthwise rods 105, 105′, 106 in the shape of a long, thin steel curve are aligned at a predetermined interval between horizontal hitching racks 104, 104′ held onto the front horizontal part 102. The lengthwise rods 105, 105′, 106 are inter-connected by horizontal rod 108. Rear hitching racks 114 are constructed with center part 110 in parallel to the horizontal rod 108 at the rear end of the horizontal hitching racks 104, 104′, and vertical parts 112, 112′ vertically extended and bent at both ends of the center part 110.

[0083] At this time, the horizontal hitching racks 104, 104′ are stretched far at their front side to prevent any horizontal movement of the shelf. Front loops 116, 116′ are formed at the ends of the horizontal hitching racks 104, 104′ to be hitched to both ends of the front horizontal part 102. The rear loops 118, 118′ are formed at the rear ends of the horizontal hitching racks 104, 104′, and the bent parts of the rear hitching racks 114 are shaped to be rotated and coupled with the rear loops 118, 118′.

[0084] The rear end of the lengthwise rods 105, 105′ is bent upwards. The front end of the vertical rod 106 are bent downwards to prevent an easy detachment, after being assembled, even when the chair is tilted. At this time, the downwardly bent front end of the lengthwise rod 106 is hitched to the front horizontal part 102.

[0085] Loops 120, 120′ are formed at the end of the rear hitching racks 114 to be hitched to both sides of the seat rear side support part 50.

[0086] The shelf 100, as shown in FIG. 9, is completely assembled by holding the front loops 116, 116′ of the horizontal hitching racks 104. 104′ at both ends of the front horizontal part 102, pulling the rear hitching racks 114 toward the rear legs 42, 42′, turning the vertical parts 112, 112′ of the rear hitching rack 114 upwards to the counter-clock direction and hitching the loop 120, 120′ to both ends of the seat rear side support part 50.

[0087] As described above, the shelf 100 is useful for conveniently put a variety of a user's belongings, and, after complete assembly, the shelf is regarded strong enough to avoid any problem at its fixed parts when the chair is tilted.

[0088]FIGS. 10 through 12 are exploded, perspective views for illustrating a stackable tilting chair in accordance with a third embodiment of the present invention.

[0089] As shown in the drawings, in the third embodiment of the present invention, a support rack 122 is extended upwards to the height of the horizontally extended part 40′ at a part where the seat front side support part 48 and the front leg 46′ meet. A writing board 124 is coupled between the horizontally extended part 40′ and the support rack 122. The user can conveniently take notes with the writing board 124. First and second fixing brackets 126, 128 are mounted at the horizontally extended part 40′ and the support rack 122 with a fastening member 125.

[0090] At this time, the support rack 122 of a rod is fixed at the upper part of the front leg 46′, extended upwards and horizontally bent to form a triangular shape, extended downwards and, finally, bent and fixed at the seat front side support part 48. In addition, a protruder 131 is formed at the straight line part 129 of the triangular shape of the support rack 122 to prevent any relative movement between the writing board 124 and the support rack 122, and the first fixing bracket 126 is restrained at the corner of the triangle of the support rack 122.

[0091] The writing board 124 is a piece of board having a straight line shaped external portion and a table tennis racket shaped inner portion. The first and second fixing brackets 126, 128 are coupled at the straight line shaped portion. Furthermore, a protruder 130 is formed at the front, upper surface of the writing board. A single line groove 132 is formed at the protruder 130 along with the width direction of the writing board for accommodating a writing tool such as a ball point pen.

[0092] A journal part 134 is formed in the middle of the first fixing bracket 126 for a contact of the straight line part 129 of the support rack, and a pair of flanges 136, 136′ are also included with through holes at both sides of the first fixing bracket 126.

[0093] The second fixing bracket 128 is formed to be foldable because its cover 138 and its body 140 are connected by a connecting part 142. Therefore, the horizontally extended part 40′ is accommodated at the journal part 143 of the body 140, the cover 138 is rotated to cover the horizontal part 40′. Then, the second fixing bracket 128 is fixed at the bottom surface of the writing board 124 with a fixing member 125. At this time, the arm support is eliminated at the horizontally extended part 40′ where the second fixing bracket 128 is coupled.

[0094] At this time, a convex part 144 is formed at the journal part 143 for relatively convenient sliding to the horizontally extended part 40′, and reinforcing ribs can be mounted at the external surface of the body 140. The convex part 146 is formed to touch the horizontally extended part 40′ even when the cover is placed.

[0095] As described above, the first and second fixing brackets 126, 128 are a little loosely coupled at the support rack 122 and the horizontally extended part 40′. As shown in FIG. 12, the writing board 124 can be folded outwards. The structure as such makes a user stand up and sit down comfortably.

[0096] Besides, as shown in FIGS. 13 through 15, U- or G-shaped cramps 152, 152′ are welded at the lower part of the support rack 122, and convex protruders 150, 150′ are formed by punching to firmly fix the support rack at the front leg and the seat front side support part.

[0097] In accordance with the third embodiment of the present invention thus constructed, a user can take notes with a pen on the writing board 124 while attending lecture or seminar without any influence of a tilted chair because the writing board is firmly fastened, even if there may be a slight movement of the back support and arm holders when the chair is tilted by the user. At this time, a writing tool is conveniently accommodated at the line groove formed at the front portion of the writing board 124, so that the line groove 132 is useful for storing the writing tool while the user stop taking notes and for using it again later.

[0098]FIG. 16 illustrates an elevation view of a tilting chair with its shelf and writing board coupled altogether when the chair is tilted.

[0099] As shown in the drawing, if a user puts pressure onto the back support 32 of the support board 34, the chair changes from its shape marked in a straight line state to its shape marked in a dot line, while maintaining its tilted state.

[0100] At this time, the first fixing bracket 126 prevents a relative movement to the straight line part 129 of the support rack 122 with the protruder 131, but the second fixing bracket 128 moves relatively to the horizontally extended part 40′ for an easy tilting function of the chair.

[0101] Furthermore, the rear hitching rack 114 of the shelf is freely rotated at the rear loop 118 of the horizontal rack 104, so that the shelf may change its shape depending on the tilting of the chair, which makes the tilting of the chair easier. The front part of the vertical rod 106 is restrained by the middle part of the front horizontal part 102, thereby effectively prevent detachment of the shelf.

[0102] As described above, there are advantages in the tilting chair of the present invention in that a user feel comfortable without any pressure onto his back when he stretches his body backwards because the chair is tilted, in that the chair has a function to easily control its tilting strength and range depending upon a user and in that the chair can maintain its tilted angle with even a small degree of strength.

[0103] Besides, the tilting chair of the present invention has another advantage in performing its original tilting function without any influence from a shelf, on which a user puts materials, and a writing board, on which the user makes notes. 

What is claimed is:
 1. A tilting chair comprising: a support board integrating a seat and a back support to be elastically transformable backwards when pressure is applied to the back support; a frame which comprises a back support part tightly, horizontally coupled at the external surface of the back support, a pair of rear legs bent downwards and extended at both left and right sides of the back support part, a pair of feet bent at edges of the rear legs and extended forwards, a pair of front legs extended upwards from the front edges of the feet, a seat front side support part bent and extended to face at both upper ends of the front legs to support front portion of the seat, and a seat rear side support part interconnecting the center of the rear legs to support the rear portion of the seat; flanges longitudinally coupled at the bottom surface of the seat; a first coupling unit mounted at the front side of the flanges to fix the seat front side support part; and a second coupling unit mounted at the rear side of the flanges to fix the seat rear side support part; wherein the second coupling unit has a head part, a tail part and a hitching protruder formed at the end of the tail part to allow the seat rear side support part to slide along the tail part within a range between the head part and the hitching protruder.
 2. The chair, as defined in claim 1, further comprising: a flange unit mounted on the external surface of the back support and formed with a plurality of flanges positioned at a predetermined interval; a pair of bushes fit with the flange unit and releasably coupled each other to insert the back support part therebetween; and a third coupling unit having a plurality of wings to be tightly fit between the flanges of the flange unit.
 3. The chair, as defined in claim 1 or 2, wherein the back support of the support board comprises a plurality of long holes formed to make a user easily lift the chair; a concave part is formed at a portion where the seat and back support meet and grooved to horizontally face each other to allows the back support 32 to easily transform when the back support is applied to pressure; and the front end of the seat of the support board is formed with a downwardly curved surface to prevent the front end of the seat from pressing onto the user's thigh.
 4. The chair, as defined in claim 1 or 2, wherein pairs of shoes are respectively coupled at both sides of the feet with hitching protruders formed to face each other for easy hitching of another chair.
 5. The chair, as defined in claim 1 or 2, further comprising; a front horizontal part extended in parallel to the seat front side support part from the center of the front legs; and a shelf whose a front portion is hitched to the front horizontal part and a rear portion is hitched to the seat rear side support part; wherein the shelf further comprises horizontal hitching racks hitched to the front horizontal part and rear hitching racks rotatively coupled with a vertical part at the rear side of the horizontal hitching racks and hitched to the seat rear side support part.
 6. The chair, as defined in claim 1 or 2, wherein a pair of horizontally extended parts is extended to a predetermined length in parallel to the seat at both left and right ends of the back support part; the pair of rear legs is extensively bent toward the floor from the end of the horizontally extended parts; a support rack is coupled at a part where the seat front side support part and the front leg meet and extended upwardly to the height of the horizontally extended part, a writing board is coupled at the horizontally extended part and the support rack for easy writing; the upper portion of the support rack is coupled with the writing board by a first fixing bracket; the horizontally extended part is coupled with the writing board by a second fixing bracket, the first fixing bracket is restricted on a relative movement with the support rack by using the protruder formed at the support rack when the chair is tilted; and the second fixing bracket is coupled to relatively slide with the horizontally extended part when the chair is tilted. 